Chih-i stresses that the essential teaching of the Buddha is expressed in the Lotus Sūtra, and that it refers to the “Cause and Effect of the Buddha’s Self-cultivation” (Fo Tzu-hsing Yin-kuo) in an incalculable past of the Origin (Pen) when the Buddha initially attained Buddhahood. The initial practice of the Buddha is the cause of Buddhahood, and the initial enlightenment of the Buddha is the effect of Buddhahood. This teaching is essential because it concerns the Buddha’s initial practice for attaining Buddhahood and his initial attainment of Buddhahood. This is the foundation of all the activities of the historical Buddha in the Traces (Chi). The difference between the substance as the Ultimate Truth and the gist as the cause and effect of the Buddha’s Self-cultivation is that the substance is the foundation upon which the gist can be realized. (Vol. 2, Page 15-16)